Pipe organs can be very large instruments with thousands of pipes. Usually, each organ pipe is equipped with a pallet which closes and opens the pipe to the passage of air therethrough. When the pallet is opened, the air flow can enter the pipe and as a result a sound is produced. The pallet is opened when the organist presses the corresponding key on the organ keyboard.
Modern pipe organs use electromagnets to open a pallet when the corresponding key is pressed: pressing a key sends a current to the solenoid of the electromagnet that pulls open a moveable armature of the electromagnet. Since the armature is connected to the pallet, moving the armature causes the pallet to open. In order to control the assembly of the electromagnets that actuate the numerous pallets, an electric control system is also a part of the organ as a whole. Because of the numerous pallets an organ can have, current control systems can be however quite cumbersome.
Current electromagnet systems used for controlling the closing and opening of pallets function according to an ON/OFF principle, i.e. the pallet is either opened or closed. Pipe organs containing such electromagnet systems are therefore insensitive to the subtlety and intensity of an organist's touch to the keys.